Nowadays, many electrical appliances are widely used with computers due to the amazing power of computers. For example, video compact disks (VCDs) and digital versatile disks (DVDs) are able to be played by a personal computer. Since the size of a typical computer monitor is not large enough to exhibit the spectacular video effect of the VCD or DVD disks, it is preferred that the signals be outputted from the personal computer to a TV set to be displayed on the relatively large TV screen. The purpose can be achieved by employing a display adapter.
FIG. 1A is a partial functional block diagram of a typical display adapter. The pixel parallel digital signals from a graphic chip 10 are selectively converted into a proper format of analog signals via either a random access memory digital-to-analog converter (RAM DAC) 11 or a TV encoder 12, and delivered to a computer monitor 13 or a TV screen 14, respectively, for display. Further, for TV analog signals, two formats, i.e. the NTSC (National Television Standards Committee) standard and the PAL (Phase Alternate Line) standard, are involved.
The functional block diagram of the TV encoder 12 can be seen in FIG. 1B. The pixel parallel digital signals from the graphic chip 10 is processed by a data capture device 121, a color space converter 122, a scaler and deflicker 123, an NTSC/PAL encoder 124 and a digital-to-analog converter 125 to produce the TV analog signals either in the NTSC or PAL standard.
The functional block diagram of a conventional scaler and deflicker 123 can be seen in FIG. 1C. In the NTSC standard and the PAL standard, the numbers of horizontal scan lines are 525 and 625 per frame, respectively, either of which is different from that in the computer monitor standard, e.g. 600 per frame or 768 per frame. Thus, the image data outputted from the color space converter 122 needs to be scaled to be of a proper number of horizontal scan lines by a scaler 1231. The scaling step is usually proceeded by a bilinear algorithm. For example, when five scan lines are scaled into four scan lines, the color space values of the resulting second scan line correlates to those of the original second and third scan lines. Likewise, the color space values of the resulting third scan line correlates to those of the original third and fourth scan lines. For easily understanding the bilinear algorithm operation, each scan line mentioned in the above is represented by a pixel, and the conversion is illustrated as shown in FIG. 2A. The color space values of the resulting pixel P41 is equal to that of the original pixel P51. The color space values of the resulting pixels P42, P43 and P44 are obtained by the operations of 3(P52)/4+1(P53)/4, 2(P53)/4+2(P54)/4 and 1(P54)/4+3(P55)/4, respectively, in which (P52), (P53), (P54) and (P55) are respective color space values of the original pixels P52, P53, P54 and P55. In addition, because the TV frame is displayed in a manner of interlacing scanning, the scaled image data needs to be divided into two fields, i.e. an odd field and an even field, which are interlacingly displayed. Hence, when a non-interlacingly scanned image data is converted into an interlacing image data, a horizontal scan line of a single pixel height only appears in one of fields so as to cause a flicker phenomenon when displaying. For ruling out this phenomenon, a deflicker 1232 performs a filter process with a predetermined coefficient of [¼, ½, ¼] on each of received horizontal scan lines. In other words, each horizontal scan line is re-defined by weightingly calculating an immediately above and an immediately below scan lines, and the scan line itself. Please refer to the pixels shown in FIG. 2B. The color space value of the pixel P2′ is re-defined by (P1)/4+(P2)/2+(P3)/4, in which (P1), (P2), and (P3) are respective color space values of the original pixels P1, P2, and P3. Therefore, the color feature of the scan line will appear in both fields, so the flicker phenomenon can be avoided or minimized.
Along with the increasing number of horizontal scan lines in each computer monitor frame, for example up to 768, 864, 1024 or even 1200 scan lines, the scaler 1231 needs to proceed a quite large vertical reduction rate. When the scaling factor is down to a value smaller than about 0.7, the line-loss problem could occur. That is, some horizontal scan lines will not be referred by any of the re-defined scan lines, or the re-defined image data will not incorporate therein the data of the lost line. As shown in FIG. 2C, the pixel P12 indicates a lost pixel that is referred by neither the pixel P22 nor the pixel P21. Thus, the color data of P12 will be lost because of the scaling procedure, resulting in a poor image quality. Furthermore, the image quality will become worse after the color data is processed by the aforementioned deflickering operation of the device 1232.
Therefore, the purpose of the present invention is to develop a method and a device for adaptively deflickering to deal with the above situations encountered in the prior art.